getutent, getutid, getutline, pututline, setutent, endutent, utmpname - user
accounting database functions
struct utmp *getutent(void);
struct utmp *getutid(const struct utmp *id);
struct utmp *getutline(const struct utmp *line);
struct utmp *pututline(const struct utmp *utmp);
int utmpname(const char *file);
These functions provide access to the user accounting database, utmp.
Entries in the database are described by the definitions and data structures
The utmp structure contains the following members:
char ut_user; /* user login name */
char ut_id; /* /sbin/inittab id */
/* (usually line #) */
char ut_line; /* device name (console, lnxx) */
short ut_pid; /* process id */
short ut_type; /* type of entry */
struct exit_status ut_exit; /* exit status of a process */
/* marked as DEAD_PROCESS */
time_t ut_time; /* time entry was made */
The structure exit_status includes the following
short e_termination; /* termination status */
short e_exit; /* exit status */
The getutent() function reads in the next entry from a utmp
database. If the database is not already open, it opens it. If it reaches the
end of the database, it fails.
The getutid() function searches forward from the current point in the
utmp database until it finds an entry with a ut_type matching
id->ut_type if the type specified is RUN_LVL,
BOOT_TIME, DOWN_TIME, OLD_TIME, or NEW_TIME. If
the type specified in id is INIT_PROCESS, LOGIN_PROCESS,
USER_PROCESS, or DEAD_PROCESS, then getutid() will return
a pointer to the first entry whose type is one of these four and whose
ut_id member matches id->ut_id. If the end of database
is reached without a match, it fails.
The getutline() function searches forward from the current point in the
utmp database until it finds an entry of the type LOGIN_PROCESS
or ut_line string matching the line->ut_line string.
If the end of database is reached without a match, it fails.
The pututline() function writes the supplied utmp structure into
the utmp database. It uses getutid() to search forward for the
proper place if it finds that it is not already at the proper place. It is
expected that normally the user of pututline() will have searched for
the proper entry using one of these functions. If so, pututline() will
not search. If pututline() does not find a matching slot for the new
entry, it will add a new entry to the end of the database. It returns a
pointer to the utmp structure. When called by a non-root user,
pututline() invokes a setuid() root program to verify and write
the entry, since the utmp database is normally writable only by root.
In this event, the ut_name member must correspond to the actual user
name associated with the process; the ut_type member must be either
USER_PROCESS or DEAD_PROCESS; and the ut_line member must
be a device special file and be writable by the user.
The setutent() function resets the input stream to the beginning. This
reset should be done before each search for a new entry if it is desired that
the entire database be examined.
The endutent() function closes the currently open database.
The utmpname() function allows the user to change the name of the
database file examined to another file. If the file does not exist, this will
not be apparent until the first attempt to reference the file is made. The
utmpname() function does not open the file but closes the old file if
it is currently open and saves the new file name.
A null pointer is returned upon failure to read, whether for permissions or
having reached the end of file, or upon failure to write. If the file name
given is longer than 79 characters, utmpname() returns 0.
Otherwise, it returns 1.
These functions use buffered standard I/O for input, but pututline() uses
an unbuffered non-standard write to avoid race conditions between processes
trying to modify the utmp and wtmp databases.
Applications should not access the utmp and wtmp
databases directly, but should use these functions to ensure that these
databases are maintained consistently. Using these functions, however, may
cause applications to fail if user accounting data cannot be represented
properly in the utmp structure (for example, on a system where PIDs
can exceed 32767). Use the functions described on the getutxent(3C)
manual page instead.
See attributes(7) for descriptions of the following attributes:
The most current entry is saved in a static structure. Multiple accesses require
that it be copied before further accesses are made. On each call to either
getutid() or getutline(), the function examines the static
structure before performing more I/O. If the contents of the static structure
match what it is searching for, it looks no further. For this reason, to use
getutline() to search for multiple occurrences, it would be necessary
to zero out the static area after each success, or getutline() would
just return the same structure over and over again. There is one exception to
the rule about emptying the structure before further reads are done. The
implicit read done by pututline() (if it finds that it is not already
at the correct place in the file) will not hurt the contents of the static
structure returned by the getutent(), getutid() or
getutline() functions, if the user has just modified those contents and
passed the pointer back to pututline().